llvm dev - Mar 2016 - define intrinsic function with pointer-typed parameter

Hi,

If I define a intrinsic function with pointer-typed parameter, for example,
def llvm_foo_ptr_ty        : LLVMPointerType<llvm_i16_ty>;
def int_foo_get : Intrinsic<[llvm_foo_ptr_ty], [llvm_foo_ptr_ty,
llvm_i32_ty], [IntrReadArgMem]>;

How to lower it for the backend? I'm not sure what kind of register (i16 or
i32 or i32) is needed in this case? If the parameter is
LLVMPointerType<llvm_i32_ty> instead of
LLVMPointerType<llvm_i16_ty>, will
this make difference for the backend? Suppose my backend has three types of
register: i16, i32, i64.

When I check the debug information, I can see LLVM tries to use i32 to
lower the parameter to build SDAG. But why it chooses i32 instead of i64?

Any input is appreciable.

Regards,

Xiangyang
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It sounds like you're hitting the default case in 
SelectionDAGBuilder::visitIntrinsicCall and exercising the 
visitTargetIntrinsic code path.  I haven't dug into the default handling 
there, but that's probably what you need to look at. Depending on your 
intrinsic, you might also consider adding custom handling in 
visitIntrinsicCall itself.

On 03/21/2016 04:33 PM, Xiangyang Guo via llvm-dev
wrote:
> Hi,
>
> If I define a intrinsic function with pointer-typed parameter, for 
> example,
> def llvm_foo_ptr_ty        : LLVMPointerType<llvm_i16_ty>;
> def int_foo_get : Intrinsic<[llvm_foo_ptr_ty], [llvm_foo_ptr_ty, 
> llvm_i32_ty], [IntrReadArgMem]>;
>
> How to lower it for the backend? I'm not sure what kind of register 
> (i16 or i32 or i32) is needed in this case? If the parameter is 
> LLVMPointerType<llvm_i32_ty> instead of
LLVMPointerType<llvm_i16_ty>,
> will this make difference for the backend? Suppose my backend has 
> three types of register: i16, i32, i64.
>
> When I check the debug information, I can see LLVM tries to use i32 to 
> lower the parameter to build SDAG. But why it chooses i32 instead of i64?
This sounds like your target isn't telling the canonicalization logic 
i16 is a valid register type or that the cost of i32 register is much 
less than an i16.  However, I'm no expert in the backend stuff, so take 
my comment with a grain of salt.
>
> Any input is appreciable.
>
> Regards,
>
> Xiangyang
>
>
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> llvm-dev at lists.llvm.org
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